I have a 94 Chrysler LeBaron, automatic, with 127,000 miles. Anytime the car sits for awhile (2 or more hours), I have to let it warm up for 15 to 20 minutes before I can get the transmission to engage. Even after letting it warm up, the tranny will still slip sometimes. I can be driving down the road and the tranny will shift into low on its own. I have to pull over and put the car into netural, shut it off, and then then restart it. After that, it will normally run ok. What could be causing this problem?